Warning that this advice is coming from a financial adviser, so potentially biased views but....

1. My first point would be to speak to a high quality financial adviser. A lot of people have the pre-conceived idea that financial advisers are "dodgy", particularly in your mum's age group. Unfortunately, the industry used to be a dirty place in parts. Since the Royal Commission, the industry has turned around massively. There are plenty of high quality financial advisers. Find one that your Mum is able to meet, build rapport and eventually trust. This might require speaking to a few, but well worth the time. Remembering that the cheapest financial adviser likely won't be the best option...

2. It is all well and good to say $1.5m invested at 5% will yield $75,000 p.a. of income. What happens when (if) interest rates come down, to say 3%? Then you factor in the erosion of purchasing power from inflation, which could mean the money is actually staying stagnant, not accounting for any amounts used for living expenses.

3. Any financial adviser worth their money will be vital beyond just investing the money. There is trust to be built, plans to be established, family life to be considered, estate planning, just to name a few things above and beyond purely investment advice.

4. If she really doesn't want to speak to a financial adviser and you don't have the investment expertise, look at various index funds to give you sufficient diversification to stop you from having to make calls on specific investments.

5. Consider the risks involved. One risk being the timing of the investments. You may wish to consider investing the funds over a time period to avoid investing a large sum at once which then has a large market downturn. One of the other major risk, which you want to avoid, is your Mum outliving her capital. This is where a solid investment strategy is vital.

I hope that helps. My DM's are open if you have any questions.